cases, one large plane, one small, with different landing systems but one manufacturer, bombardier of canada. federal records show in the last two years, there have been only two such incidents involving airliners made by other companies but in that time you have the six bombardier incidents, two in the last four days plus chicago, atlanta, ontario, california, and philadelphia. in each case, the planes landed safely without injuries to those on board, but with that many accidents involving similar aircraft made pie by the same company, authorities want to know if that's a pattern. the f.a.a. and national transportation safety board are investigating and aviation investigators say wear and tear could be an issue. >> they're designed and used for short-haul uses of passengers so they may take off and land three five, seven, 10 times a day sometimes. so their landing gear are put under a lot more stress. >> reporter: today bombardier said it would support any investigation. dean reynolds, cbs news, chicago. >> couric: in health news, there's been a lot of debate about what causes attention def